Yes that would work.
Quote from the Eve-wiki
here:
PLEX can be used by players regardless of the type of account they have. When you activate a PLEX, the extra time is added to your account immediately. In this respect, PLEX works exactly like a prepaid game time code.
If you are currently using a Trial account, your account is converted to a paying account and the 30 days are added onto the remaining days left in your trial period.
They're very simple you use, once you have the plex, you can right-click it, then select 'add game time to account' which will add the 30days gametime. This can also be done from anywhere within the universe, you do not have to be in the station where the PLEX is located. Use the assets window to do this.